boot time regressed a lot due to misaligned access probe

[Jisheng Zhang]

On Wed, Sep 13, 2023 at 11:46:28AM +0100, Ben Dooks wrote:
> On 13/09/2023 01:14, Jisheng Zhang wrote:
> > Hi all,
> > 
> > Probing one cpu for misaligned access cost about 0.06s, so it will cost
> > about 3.8s on platforms with 64 CPUs, for example, milkv pioneer which
> > is powered by sg2042.
> > 
> > I'm not sure the reason of probing misaligned access for all CPUs. If
> > the HW doesn't behave as SMP from misalligned access side, then unless
> > userspace processes force cpu affinity, they always suffer from this
> > non-SMP pain.
> > 
> > So, can we only probe the boot cpu?
> 
> So a couple of ideas:
> 
> #1 is it worth adding a device-tree property to explicitly to say if
> the unaligned access has been measured and known
> 
> #2 only probe one cpu in a cluster if there are multiple clusters of
> cpus?

and #3 Could userspace who cares about misaligned access probe the
speed itself? And this reminds me the arm case: old armv5te VS armv7,
there's no such probe in arm yet.

> 
> -- 
> Ben Dooks				http://www.codethink.co.uk/
> Senior Engineer				Codethink - Providing Genius
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